[PATCH v2 0/6] Enable setexpr command to print cpu-list like bitmaps

[Heinrich Schuchardt]

On 12.12.23 12:56, Lukas Funke wrote:
> On 12.12.2023 12:40, Heinrich Schuchardt wrote:
>> On 12.12.23 11:13, Heinrich Schuchardt wrote:
>>> On 12.12.23 09:52, lukas.funke-oss at weidmueller.com wrote:
>>>> From: Lukas Funke <lukas.funke at weidmueller.com>
>>>>
>>>>
>>>> This series enables the 'setexpr' command to print "cpu list"-like
>>>> bitmaps based on the printk format specifier [1].
>>>>
>>>> One use-case is to pass cpu list [2] based kernel parameter like
>>>> 'isolcpu', 'nohz_full', irq affinity or RCU related CPU parameter to
>>>> the kernel via a separate firmware variable without exposing the
>>>> 'bootargs' variable to directly.
>>>>
>>>> Example:
>>>>
>>>> setexpr isolcpu_bootarg=%32pbl $myCPUisolation
>>>
>>> I applied your patches on top of origin/next but your example simply
>>> does not work:
>>>
>>> => setenv myCPUisolation 123456789abcdef0
>>> => setexpr isolcpu_bootarg=%32pbl $myCPUisolation
>>> ## Error: illegal character '='in variable name "isolcpu_bootarg=%32pbl"
>>>
>>> This produces some output:
>>>
>>> => setexpr a fmt '%32pbl' 64; echo $a
>>> 6
>>>
>>> But the result is completely unexpected. Number arguments in U-Boot are
>>> always hexadecimal. So the output should be
>>>
>>> 2,5-6
>>
>> doc/usage/cmd/setexpr.rst
>>
>> has an example showing this.
>>
>>      => setexpr foo fmt 0x%08x 63
>>      => echo $foo
>>      0x00000063
>>      =>
>>
>> You provide a use case for %pbl but not an reason why you want to
>> support %pb. If you wanted to use the output in a device-tree
>> manipulation the %pb output would have to be big-endian formatted.
>
> I added it to be consistent with the kernel printk. Currently there is
> no use case for it. Shall we remove the %pb or leave it in for consistency?

As long as we don't know if usage requires big-endian or little-endian I
would keep it out.

Looking at the %pbl use case: What sources of the value to convert do
you envision? When the argument is a pointer, e.g.

   setexpr a fmt '%128pbl' *$fdtcontroladdr

you seem to expect that the 32bit tuples are stored in low endian order.

Please, test the output of a 64bit number on a big-endian system. You
must not assume a unsigned long long to be stored as 32bit tuples in low
endian order here.

The output does not match what is in memory. This needs to be fixed:

=> setexpr a fmt '%128pbl' *0x8bae060; echo $a
64,66,69-72,74,76,79,82,85-87,89,91-92,94,96-98,108,110,112,114,117,119,121,123,125,127
=> setexpr a fmt '%128pb' *0x8bae060; echo $a
feedf00d,deadbeef,00000000,00000000
=> mm.l 8bae060
08bae060: edfe0dd0 ?
08bae064: 92ac0000 ?
08bae068: 78000000 ?
08bae06c: 208a0000 ?

Here is another wrong output:

   =>  setexpr a fmt '%128pb' 0x92acd00dfeed; echo $a
   feedf00d,deadbeef,000092ac,d00dfeed

Expected output is

   00000000,00000000,000092ac,d00dfeed

A buffer overrun occurs. You are reading memory after the u64 value that
you create internally. To do it correctly you need to copy the u64 value
into a 128 bit buffer that has been zeroed out.

Best regards

Heinrich

>
> Best regards
> Lukas
>
>>
>> Best regards
>>
>> Heinrcih
>>
>>>
>>>> && env set bootargs "$isolcpu_bootarg"
>>>> && bootm
>>>>
>>>> [1] https://www.kernel.org/doc/Documentation/printk-formats.txt
>>>> [2]
>>>> https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
>>>>
>>>>
>>>> Changes in v2:
>>>> - Add bitmap format specifier to documentation
>>>>
>>>> Lukas Funke (6):
>>>>    sandbox: add generic find_next_zero_bit implementation
>>>>    linux: bitmap.h: add 'for_each_set_bitrange' iteration macro
>>>>    test: cmd: setexptr: Add tests for bitmap string format
>>>>    doc: printf() codes: Add bitmap format specifier
>>>>    lib: vsprintf: enable '%*pb[l]' format specifier
>>>>    cmd: printf: forward '%p' format string specifier
>>>>
>>>>   arch/sandbox/include/asm/bitops.h | 16 ++++++-
>>>>   cmd/printf.c                      | 29 ++++++++++++
>>>>   doc/develop/printf.rst            |  6 +++
>>>>   include/linux/bitmap.h            |  7 +++
>>>>   lib/vsprintf.c                    | 75
>>>> +++++++++++++++++++++++++++++++
>>>>   test/cmd/setexpr.c                |  9 ++++
>>>>   6 files changed, 140 insertions(+), 2 deletions(-)
>>>>
>>>
>>
>